Ofcom has extended its investigation into the real-world speeds homeowners get from fixed-line broadband, after signing a new contract with broadband monitoring company SamKnows.

SamKnows said on Thursday it is looking for volunteers to provide data for the project, which follows an earlier study for Ofcom. In its report last year on fixed broadband speed data, Ofcom found that UK homes on average had download speeds of 4.1Mbps, compared with ISPs' advertised speed of up to 7.1Mbps on average.

The company noted that the original study had highlighted clear discrepancies between advertised broadband speeds and what users were receiving.

"What we're looking to measure in the forthcoming project is how this ISP performance will improve as consumers switch to services which are being advertised as significantly faster," said SamKnows chief executive Alex Salter in a statement.

Under a new contract with Ofcom, SamKnows will collect data on UK fixed-line broadband speeds for two years, to April 2012. The company said it expects speeds to change significantly during that time, as ISPs such as Virgin Media and BT roll out faster cable, ADSL and fibre optic-based services.

Volunteers, who can sign up via SamKnows's website, will receive a 'White Box' monitoring device that sits in their home. The box will connect to the volunteer's network and track the performance of their broadband connection.

People will have access to their own speed-tracking data. The device does not monitor the home network or the user's web traffic, according to SamKnows.

Virgin Media said this week it plans to start rolling out a cable-based broadband service providing speeds of up to 100Mbps to homes by the end of this year, while BT plans to introducing 100Mbps fibre-to-the-home services.